I need advice on this design. EG mill head with spindle.


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Thread: I need advice on this design. EG mill head with spindle.

  1. #1

    Default I need advice on this design. EG mill head with spindle.

    So I am building an EG cnc, (never heard that one before) EG is the frame that "holds" mounting points for linear rails. The entire machine is cad'd, parts have been chosen, etc. But, I have one issue that I have run into in terms of design. I have ZERO experience with cnc mill heads and the forces they are likely put under. EG doesn't have the best tensile strength, so the majority of the structure head will have to be some sort of metal.Ideally, I get a head cast at a foundry, and design voids to be filled with EG. But, after talking to two foundry's in my state, I can't justify the upfront cost needed for a part that may not work and that I may only need one of. Here is my thrown together solution. Ideally, the machine can handle high carbon steels, but that is the upper end that I am looking for.


    The Machine:


    • Will be around the size of a tormach 440
    • nema 34, 5mm pitch ballscrew
    • 1.1hp bldc motor
    • The spindle is about 240mm long for a sense of scale.







    This these are 1/2" (insert material here) plates, it can be grey iron if i can find it in plate, or steel, this is why I am here.

    • Instead of screws, could I weld the plates?(material allowing)
    • If i welded, how would I adjust for the deformation due to heat?


    I know this is nowhere near sturdy enough, it is the "structure" i was referring too.



    I would cast in the EG after the plates are indicated in, etc. I would also have screws coming out of the plates that would sick into the EG to make sure they EG has a "firm grip" on the plates.
    • Could this be enough?
    • Or is there to little info on my EG or the forces this head is required to handle?




    I added a right angle plate for further support, this is because I have no idea what I am doing would rather over engineer when possible than under engineer.
    • Would welding this in cause too much deformation?
    • I could screw it in, with proper placement, could this serve as an adjustment?
    • Do you think this will be sturdy or rigid enough to survive cutting forces?


    Similar Threads:
    Attached Thumbnails Attached Thumbnails I need advice on this design. EG mill head with spindle.-spindle-plate-v6-jpg   I need advice on this design. EG mill head with spindle.-spindle-plate-view1-jpg   I need advice on this design. EG mill head with spindle.-spindle-plate-vierw-2-jpg   I need advice on this design. EG mill head with spindle.-spindle-plate-view-5-jpg  



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    Default Re: I need advice on this design. EG mill head with spindle.

    None of those designs look particularly rigid. Why are you extending the spindle out so far? The more extension it has, the more leverage it will exert to amplify vibrations at the tool-tip. Instead of basing it on a piece of angle, why not use a piece of channel instead? That will allow it to stabilize the spindle cartridge in two places instead of one.

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    Default Re: I need advice on this design. EG mill head with spindle.



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    Default Re: I need advice on this design. EG mill head with spindle.

    Thanks for this link



  5. #5

    Default Re: I need advice on this design. EG mill head with spindle.

    The yas axis has about 200mm of travel, and the rail for the axis has about 1 inch spacing from the z column. It sticks out that much so that the tool can reach the center of the t-slot table.

    The c channel is a good idea. I may use 2 if i can fit it.



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    Default Re: I need advice on this design. EG mill head with spindle.

    The purpose of using epoxy granite is to get a more favorable result from this equation: dampening coefficient*modulus of elasticity/density.


    To calculate what percentage of forces are exerted on the metal, or epoxy granite, by the cutting tool, you need to calculate the moment of inertia of those components and where they are located relative to the centroid of the complete assembly.


    An additional problem: in the first post's photos, it is relatively easy to imagine that the black epoxy granite will peal away from the steel plate the moment the spindle is pulled downwards. this isn't merely because the epoxy doesn't stick to the steel very well, but because all of the stress will be concentrated at the sharp corner.



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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by WolfmansBrother View Post
    So I am building an EG cnc, (never heard that one before) EG is the frame that "holds" mounting points for linear rails. The entire machine is cad'd, parts have been chosen, etc. But, I have one issue that I have run into in terms of design. I have ZERO experience with cnc mill heads and the forces they are likely put under. EG doesn't have the best tensile strength, so the majority of the structure head will have to be some sort of metal.Ideally, I get a head cast at a foundry, and design voids to be filled with EG. But, after talking to two foundry's in my state, I can't justify the upfront cost needed for a part that may not work and that I may only need one of. Here is my thrown together solution. Ideally, the machine can handle high carbon steels, but that is the upper end that I am looking for.

    .


    The Machine:


    • Will be around the size of a tormach 440
    • nema 34, 5mm pitch ballscrew
    • 1.1hp bldc motor
    • The spindle is about 240mm long for a sense of scale.







    This these are 1/2" (insert material here) plates, it can be grey iron if i can find it in plate, or steel, this is why I am here.

    • Instead of screws, could I weld the plates?(material allowing)
    • If i welded, how would I adjust for the deformation due to heat?


    I know this is nowhere near sturdy enough, it is the "structure" i was referring too.



    I would cast in the EG after the plates are indicated in, etc. I would also have screws coming out of the plates that would sick into the EG to make sure they EG has a "firm grip" on the plates.
    • Could this be enough?
    • Or is there to little info on my EG or the forces this head is required to handle?




    I added a right angle plate for further support, this is because I have no idea what I am doing would rather over engineer when possible than under engineer.
    • Would welding this in cause too much deformation?
    • I could screw it in, with proper placement, could this serve as an adjustment?
    • Do you think this will be sturdy or rigid enough to survive cutting forces?
    This is kind of a recipe for adding a lot of vibration to the machine. The EG is inadequately supported. If you have no other choice to do it that far out you must eliminate nearly all of the mass out side of the spindle housing and stiffen up the weldment or boltment between the mounting plate and the spindle. IF you can make a pyramidal shape with thick steel that tapers towards the spindle housing so the further you get away from the ways the less mass there is that would help. And then fashion a half cylindrical surface at the narrow end of the pyramid shape for the spindle housing to lay in with a couple of stout clamps to hold it there. Then pour EG into the steel pyramid shape. That might be your best bet if you can't redesign the machine. Your method might be OK for engraving but will be not so good for milling where the cutting forces can be quite high.

    A very stiff low mass design might actually be the best for what your doing. So you might want to use 20-25mm aluminum with a small amount of EG to damp it



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    Default Re: I need advice on this design. EG mill head with spindle.

    Something like this might work better if you are forced to have a long spindle head. Fill it full of expanding foam instead of EG to reduce mass. It will still damp vibrations pretty well.

    You could also use a combination of EG and expanding foam. If you put a baffle inside the pyramid about six inches out you could probably use EG near the base of the pyramid and the lighter expanding foam near the spindle area.

    If you had a cross section of internal braces, this shape could be extremely rigid. I think that you need to think in terms of making the structure stiff enough to use without the EG. Then if you can add some EG and/or expanding foam to
    help dampen vibrations you have a functioning system.

    Attached Thumbnails Attached Thumbnails I need advice on this design. EG mill head with spindle.-long-spindle-head-concept_2-jpg  
    Last edited by Hezz; 07-14-2017 at 12:59 PM.


  9. #9

    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Eldon_Joh View Post
    An additional problem: in the first post's photos, it is relatively easy to imagine that the black epoxy granite will peal away from the steel plate the moment the spindle is pulled downwards. this isn't merely because the epoxy doesn't stick to the steel very well, but because all of the stress will be concentrated at the sharp corner.
    Even if there are screws in the bottom plate cast into the epoxy to, "anchor it?"

    Would adding walls at select locations allow me to change the "centroid" of the head?



  10. #10

    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Hezz View Post
    Something like this might work better if you are forced to have a long spindle head. Fill it full of expanding foam instead of EG to reduce mass. It will still damp vibrations pretty well.
    I don't know if I have the capabilities of making this. does the draft angles of the supports add extra support? I may end up having to go with something similar to this.



  11. #11

    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Hezz View Post

    A very stiff low mass design might actually be the best for what your doing. So you might want to use 20-25mm aluminum with a small amount of EG to damp it
    I am going to see if I can figure out how to make the shape you proposed. I agree that this design won't work for milling, which is what I want. tis why i came here



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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by WolfmansBrother View Post
    I don't know if I have the capabilities of making this. does the draft angles of the supports add extra support? I may end up having to go with something similar to this.
    I don't know if the draft angles add support or not. The idea was to reduce the mass as much as possible out towards the spindle area. The further the mass is out away from the support of the ways and column the bigger problem it is. With this design it would be very strong since the pyramid shape makes a modified box. All sides of the structure have some support. Internal bracing to lock it with the fill material would increase the stiffness further.

    I admit it would be harder to make. Quite a bit harder. But you can cut steel or aluminum on a table saw with the right blade and if your accurate enough you could probably either screw it together or weld it. I know welding adds extra problems. I think if the walls were at least
    .5 inch thick you might be able to. You could also have the main structure be a solid steel or aluminum structure underneath and then pour a thick walled EG pyramid around that steel underlying structure.

    Actually, after a bit of thought. I think I have figured out an easy way to make it if you have access to a manual mill. You could cast a reinforced EG pyramid seperately with threaded inserts on the front and back. Then machine the back and front faces coplaner. The ways mounting plate and the spindle mount could then be bolted to the EG pyramid and they could be adjusted lightly for alignment. You would basically have to fabricate three parts that bolt together. THe EG pyramid, the steel or aluminum backplate and the spindle mounting flange.

    Last edited by Hezz; 07-14-2017 at 01:01 AM.


  13. #13

    Default Re: I need advice on this design. EG mill head with spindle.

    I need advice on this design. EG mill head with spindle.-possible-casting-v2-jpg



  14. #14

    Default Re: I need advice on this design. EG mill head with spindle.

    I may end up making what I want to cast, just out of plate. I guess i could well the structure together then get someone to bore the spindle hole. I wonder how much that would cost.



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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Hezz View Post
    Fill it full of expanding foam instead of EG to reduce mass. It will still damp vibrations pretty well.
    Can you explain?
    This is the first time I read that you can dampen machine vibrations with light weight foam

    Sven http://www.cnczone.com/forums/diy-cnc-router-table-machines/320812-aluminium-1250x1250x250-router.html


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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by WolfmansBrother View Post
    I need advice on this design. EG mill head with spindle.-possible-casting-v2-jpg
    That seems to be a lot better than the first design. But I would leave the center rib you had in there also and make it bigger with some holes in it to lock in the fill. It's still quite a lot of mass out there and your success with this may depend on how stiff the main machine is. IF the gantry or columns are large and heavy it may work well enough for non critical applications.

    Do you have a picture or a model of your mill?



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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by CaptainVee View Post
    Can you explain?
    This is the first time I read that you can dampen machine vibrations with light weight foam
    Internal cavities can be damped with sticky expanding foam. It dos not work as well as EG because it does not add much mass. But in some applications it could perform better than EG. IF the machine is not very stiff and well damped adding a high mass material in the milling head can cause all kinds of vibrational problems because the rest of the machine is not stiff enough to handle the vibration of a large
    mass. In a system like this a stiff but low mass damping system might perform better.



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    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by WolfmansBrother View Post
    I may end up making what I want to cast, just out of plate. I guess i could well the structure together then get someone to bore the spindle hole. I wonder how much that would cost.
    Are you trying to make this from home without the use of a manual mill. IF you have a drill press you may be able to make all the parts bolt together and avoid the warping that welding brings. You could make the large hole with a hole saw. It does not have to be a tight fit. What is important is that the way mounting plate and the bottom of the spindle nose plate are perpendicular to each other. You need a small surface plate or very flat setup table to do this. You could cast the fill with the spindle in place coated with a thick mold release compound so it could be removed. Or cast it permanently in place.



  19. #19

    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Hezz View Post
    You need a small surface plate or very flat setup table to do this. You could cast the fill with the spindle in place coated with a thick mold release compound so it could be removed. Or cast it permanently in place.
    I was doing everything from home, but I recently got cleared at my local makerspace to use their metal machine tools. I now have access to some surface plates, mill, cnc mill and a plethora of other tooling when I am "certified" by them.

    I am not going to cast the spindle permanently in place. I may turn down some uhmw or hpde and cast that in. The epoxy shouldn't adhere to those plastics, then mount the spindle in that.

    Quote Originally Posted by Hezz View Post
    What is important is that the way mounting plate and the bottom of the spindle nose plate are perpendicular to each other.
    I am concerned about this. I have no idea how to make this thing super perpendicular.



  20. #20

    Default Re: I need advice on this design. EG mill head with spindle.

    Quote Originally Posted by Hezz View Post
    That seems to be a lot better than the first design. But I would leave the center rib you had in there also and make it bigger with some holes in it to lock in the fill. It's still quite a lot of mass out there and your success with this may depend on how stiff the main machine is. IF the gantry or columns are large and heavy it may work well enough for non critical applications.

    Do you have a picture or a model of your mill?
    I need advice on this design. EG mill head with spindle.-possible-casting-v9-jpg

    for scale, that spindle is about 240mm. the X axis is about 600mm.

    I need advice on this design. EG mill head with spindle.-eg-cnc-jpg



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I need advice on this design. EG mill head with spindle.

I need advice on this design. EG mill head with spindle.